1. Field of the Invention
The present invention relates to a bidirectional insulated DC/AC inverter, and specifically relates to a switching control between a battery charge operation and an AC power output operation.
2. Description of the Related Art
FIG. 1 is a diagram showing an existing bidirectional insulated DC/AC inverter.
A bidirectional insulated DC/AC inverter 30 shown in FIG. 1 comprises a filter 34 comprising coils 31 and 32 and a capacitor 33, a bridge circuit 39 comprising four switching elements 35-38 and connected to the filter 34, a bridge circuit 45 comprising four switching elements 41-44 and connected to the bridge circuit 39 via a capacitor 40, a bridge circuit 51 comprising four switching elements 47-50 and connected to the bridge circuit 45 via a transformer 46, a capacitor 53 and a coil 54 provided between the bridge circuit 51 and a battery 52, a plug 55, an outlet 56, and a relay 57 electrically connecting the bridge circuit 39 and the plug 55 via the filter 34 while charging the battery 52 and electrically connecting the bridge circuit 39 and the outlet 56 via the filter 34 while outputting AC power of the bidirectional insulated DC/AC inverter 30. It should be noted that the switching elements 35-38, the switching elements 41-44, and the switching elements 47-50 are, for example, IGBT (Insulated Gate Bipolar Transistors), and a diode is connected in parallel with each of the switching elements. It is assumed that the plug 55 is connected to an outlet 59, comprised in an external power source 58 while charging the battery 52. The outlet 56 is connected to a plug 61, comprised in an external load 60 while outputting AC power from the bidirectional insulated DC/AC inverter 30.
The bidirectional insulated DC/AC inverter 30, when charging the battery 52, turns the switching elements 41 and 44 and the switching elements 42 and 43 of the bridge circuit 45 on and off in an alternate manner. In other words, when the battery 52 is charged, the AC power input to the bridge circuit 39 from the power source 58 via the outlet 59, the plug 55, the relay 57, and the filter 34 is converted into DC power after being rectified by the diodes connected in parallel with the switching elements 35-38 of the bridge circuit 39 and being made smoothed by the capacitor 40. Next, the DC power is converted into AC power by the bridge circuit 45 and afterwards output to the bridge circuit 51 via the transformer 46. The AC power is rectified by the diodes connected in parallel with the switching elements 47-50 of the bridge circuit 51, is made smoothed by the capacitor 53, and afterwards is converted into DC power. The DC power is provided to the battery 52 via the coil 54.
The above bidirectional insulated DC/AC inverter 30, when supplying AC power to the load 60, turns the switching elements 47 and 50 and the switching elements 48 and 49 of the bridge circuit 51 on and off in an alternate manner, as well as turning the switching elements 35 and 38 and the switching elements 36 and 37 of the bridge circuit 39 on and off in an alternate manner. In other words, when AC power is supplied from the bidirectional insulated DC/AC inverter 30 to the load 60, the DC power obtained from the battery 52 is converted into AC power by the bridge circuit 51, and is output to the bridge circuit 45 via the transformer 46. Next, the AC power is rectified by the diodes connected in parallel with the switching elements 41-44 of the bridge circuit 45, is made smoothed by the capacitor 40, and is converted into DC power. The DC power is converted into AC power by the bridge circuit 39 and is provided to the load 60 via the filter 34, the relay 57, the outlet 56, and the plug 61.
As described above, the bidirectional insulated DC/AC inverter 30 drives the bridge circuit 45 while charging the battery 52 and drives the bridge circuit 39 and the bridge circuit 51 while outputting AC power (for an example, please see Patent Document 1).
Patent Document 1:
Japanese Patent Application Publication No. 2001-37226
However, since the relay 57 of the bidirectional insulated DC/AC inverter 30 is a mechanical switch, it is likely to cause operation error at the end of the product-life cycle owing to repeated opening and closing. Thus, there is a risk of malfunction of the bidirectional insulated DC/AC inverter 30 caused by operation error in the relay 57, such as the bridge circuit 39 and the plug 55 being connected while AC power output of the bidirectional insulated DC/AC inverter 30.